ServiceStack service request design

Question

I am keen on using ServiceStack and have created a little test app with a simple customer service:

  [Route("/customers/{id}")]
    public class GetCustomer : IReturn<Customer>
    {
        public int Id { get; set; }
    }
    [Route("/customers/search")]
    public class FindCustomers : IReturn<List<Customer>>
    {
        public string LastName { get; set; }
        public int Age { get; set; }
        public string? City { get; set; }
    }

    public class CustomerService : IService
    {
        public object Get(GetCustomer request)
        {
            var db = new WebServDb();
            var customer = db.FirstOrDefault<Customer>("WHERE Id=@0", request.Id);
            return customer;
        }
        public object Get(FindCustomers request)
        {
            var db = new WebServDb();
            var customers = new List<Customer>();
            if (request.City.HasValue)
                customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2", request.LastName, request.Age, request.City);
            else
                customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1", request.LastName, request.Age);
            return customers;
        }
    }

The FindCustomers request DTO contains 3 properties that can be used to search for customers. Based on which properties are set I need to query the DB differently. So what is the best way to do this? For example, if I add another property such as:

 [Route("/customers/search")]
    public class FindCustomers : IReturn<List<Customer>>
    {
        public string LastName { get; set; }
        public int Age { get; set; }
        public string? City { get; set; }
        public string? ZipCode { get; set; }
    }

to the FindCustomers DTO, I would also have to change the service Get method to:

public object Get(FindCustomers request)
{
    var db = new WebServDb();
    var customers = new List<Customer>();
    if (request.City.HasValue && request.ZipCode.HasValue)
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2 AND ZipCode=@3", request.LastName, request.Age, request.City, request.ZipCode);
    else if (request.City.HasValue)
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1 AND City=@2", request.LastName, request.Age, request.City);
    else
       customers = db.Fetch<Customer>("WHERE LastName=@0 AND Age=@1", request.LastName, request.Age);
    return customers;
  }

So for each property I add/remove from the request DTO I need to modify my Get method. Is there better way do this? A more generic way to check for properties set and querying the DB?

Would it be better to have specific request DTOs such as FindCustomersByLastNameCity, FindCustomersByLastNameZipCode, etc. as well as corresponding specific Get methods in the CustomerService?

paaschpa paaschpa · Accepted Answer · 2013-09-12T18:11:54

Would it be better to have specific request DTOs such as FindCustomersByLastNameCity, FindCustomersByLastNameZipCode
I would avoid this if possible as it goes against the 'Message Based Services' benefits/approach encouraged by ServiceStack.

Is there better way do this?
I don't know if I have a 'better way' but below are two options I have tried. The second option is still a 'work in progress' and is meant to be more 'abstract' but I modified it to work with your example and to hopefully inspire other ideas.

Option 1 using ExpressionVisitor:

public object Get(FindCustomers request)
{
    var customers = new List<Customer>();

    var ev = OrmLiteConfig.DialectProvider.ExpressionVisitor<Customer>();
    ev.Where(c => c.LastName == request.LastName).And(c => c.Age == request.Age);
    AddOptionalFilters(ev, request);

    customers = Db.Select<Customer>(ev);

    return customers;
}

private void AddOptionalFilters(SqlExpressionVisitor<Customer> expressionVisitor, FindCustomers request)
{
    if (request.City.HasValue)
    { expressionVisitor.Where(c => c.City == request.City); }

    if (request.ZipCode.HasValue)
    { expressionVisitor.Where(c => c.ZipCode == request.ZipCode); }
}

Option 2 using the SqlBuilder from Dapper:

public object Get(FindCustomers request)
{
    var customers = new List<Customer>();          

    var sqlAndParams = SqlAndParameters("SELECT * From Customers", request); //this returns a tuple of the sql string and the parameters
    customers = Db.Query<Customer>(sqlAndParams.Item1, sqlAndParams.Item2);

    return customers;
}

public virtual Tuple<String, IDictionary<string, object>> SqlAndParameters(string sql, FindCustomers request)
{
    var builder = new SqlBuilder();
    var selector = builder.AddTemplate(sql);
    var sqlParams = new ExpandoObject() as IDictionary<string, object>;

    builder.Where("LastName=@LastName");
    sqlParams.Add("LastName", request.LastName);

    builder.Where("Age=@Age");
    sqlParams.Add("Age", request.Age);

    if (request.City.HasValue)
    {
        builder.Where("City=@City");
        sqlParams.Add("City", request.City);
    }

    if (request.ZipCode.HasValue)
    {
        builder.Where("ZipCode=@ZipCode");
        sqlParams.Add("ZipCode", request.ZipCode);
    }

    return Tuple.Create(selector.RawSql, sqlParams);
}

ServiceStack service request design

1 Answers